The present invention relates to a developing unit in an image forming apparatus such as an electrophotographic copying machine or electrophotographic printer and, more particularly, to a developer regulating member adopted in a one-component developing unit which performs development by using a one-component developer, and a method of molding the same.
In a conventional electrophotographic image forming apparatus, an electrostatic latent image formed on an image carrier is made visible as a toner image by a developing unit.
As one such conventional developing unit, for example, a developing apparatus shown in FIG. 8 is known, in which a developer carrying member 103 (to be referred to as a developing sleeve hereinafter) is rotatably attached to a developer container 102 at a small distance from an electrophotographic photosensitive drum 101 rotatably supported by an apparatus main body. A developer regulating member 104 and elastic roller 105 are abutted against the developing sleeve 103. Toner 106 serving as a one-component developer is contained in the developer container 102.
In this conventional developing unit, as a means for regulating small the layer thickness of the toner 106 carried and conveyed to the developing unit by the developing sleeve 103, the developer regulating member 104 made of rubber or a metal is abutted against the developing sleeve 103. The toner 106 is regulated as it is passed through the abutting portion between the developer regulating member 104 and developing sleeve 103, so that a thin film of the toner 106 is formed on the developing sleeve 103. Also, triboelectricity for developing the latent image is applied to the toner 106 by friction at the abutting portion.
To form the thin film coating with the toner 106 on the developing sleeve 103, since the particles of the toner 106 exist with a distribution range of several xcexcm to ten-odd xcexcm, when development is to be performed by using the developer regulating member 104 and developing sleeve 103, the following two factors are particularly important.
First, it is important to urge the developer regulating member 104 against the ridge portion on the surface of the developing sleeve 103 uniformly and highly precisely so that the toner 106 sandwiched between the developing sleeve 103 and developer regulating member 104 is uniformly charged by friction, and simultaneously to form a uniform thin layer on the developing sleeve 103. For this purpose, the developer regulating member 104 must have a high flatness.
Second, it is important not to form a partial streaking nonuniformity in the thin layer on the developing sleeve 103. For this purpose, the developer regulating member 104 which urges against the developing sleeve 103 must have a small surface roughness.
When the developer regulating member 104 is made of a metal, it has a high modulus of elasticity. The urging force accordingly fluctuates largely in accordance with the urging conditions, and a preset pressure is difficult to control. Since the developer regulating member 104 is a rigid body, it is difficult to urge it uniformly along the ridge of the sleeve, and a streaking nonuniformity in the coating and the like tends to be formed on the developing sleeve 103 by partial defective urging.
When the developer regulating member 104 is made of rubber, it has a lower modulus of elasticity than the developer regulating member 104 made of a metal. The urging force accordingly fluctuates less in accordance with the urging conditions, and the preset pressure can be controlled easily. However, since this developer regulating member 104 is soft, it is difficult to set the urging position against the developing sleeve 103. When the developer regulating member 104 is used over a long period of time, creep is produced by plastic deformation in rubber to decrease the preset pressure, affecting the development efficiency.
As a countermeasure, as shown in FIG. 9, it is proposed to form a developer regulating member 104 from an elastic blade 107 and metal thin plate 108, and to stack the elastic blade 107 made of rubber or the like on the metal thin plate 108 with an adhesive 109. To stack this developer regulating member 104, the elastic blade 107 molded in advance to form a rubber piece is adhered through the adhesive 109, or the metal thin plate 108 is mounted and arranged in a mold in advance, and raw material rubber is charged into the mold and uniformly and thermally formed with a hot press. In recent years, a method of mounting and arranging a metal thin plate in a mold in advance, and injection-molding a thermoplastic elastomer in the mold is proposed, as described in Japanese Patent Laid-Open No. 8-95377.
In the developer regulating member 104 in this conventional injection molding, a gate 110 for resin injection is formed at substantially the center of the long-side end face of the elastic blade 107, as shown in FIG. 5, and a runner 111 is so formed as to continue to the gate 110. This runner 111 is a cold runner. The elastic blade 107 to be formed by charging the resin has a thin, elongated shape with a thickness of approximately 1 mm and a length of approximately 200 mm or more. The runner 111 minimizes the length of a resin flow path, thereby eliminating defective charging. If the runner 111 is a hot runner, a portion near the gate 110 thermally shrinks greatly due to the heat of the hot runner. Also, since the gate 110 is located on the long-side end face, its heat shrinkage degrades the flatness of the elastic blade 107.
The metal thin plate (e.g., phosphor bronze; 1.8xc3x9710xe2x88x926/xc2x0 C.) and thermoplastic elastomer (e.g., polyamide-containing elastomer diamide PAE E40[manufactured by DAICEL-HULS]; 1.5xc3x9710xe2x88x924/xc2x0 C.) that form the developer regulating member 104 have largely different coefficients of linear expansion. Therefore, when the thermoplastic elastomer is injected into a mold, in which the metal thin plate 108 coated with a primer is mounted and arranged in advance, to integrally mold the elastic blade 107, since shrinkage of the thermoplastic elastomer during cooling solidification is much larger than that of the metal thin plate 108, the thermoplastic elastomer on the metal thin plate 108 is fixed to the metal thin plate 108 with the primer, as shown in FIG. 6, and distortion during molding remains near the gate 110. Distortion 112 accordingly occurs between the metal thin plate 108 and gate 110 in a direction perpendicular to the long side of the elastic blade 107. This appears as a streaking nonuniformity in the coating on the developing sleeve 103 produced by partial defective urging.
As shown in FIG. 7, the resin flow changes its flowing direction after it abuts against the long side of the elastic blade 107 on the metal thin plate 108 side. As a result, a flow mark 113 is formed in the hatched portion in FIG. 7 on the surface of the elastic blade 107.
The present invention has been made to solve the above problems, and has as its object to provide a method of molding a developer regulating member having an elastic blade with a high flatness and small surface roughness, and a developer regulating member which uniformly charges toner by friction and which does not form partial streaking nonuniformity in a uniform thin layer on a developing sleeve.
In order to achieve the above object, according to the present invention, there is provided a developer regulating member obtained by integrally forming a metal thin plate with spring elasticity and an elastic blade by injection molding or injection compression molding, characterized in that a resin injection gate for the elastic blade is formed on a short-side end face of the elastic blade.
The developer regulating member according to the present invention is characterized in that a sacrificial gate is formed on a short-side end portion, opposite to the resin injection gate, of the elastic blade.
The developer regulating member according to the present invention is characterized in that the sacrificial gate has a length of not less than 1 mm.
The developer regulating member according to the present invention is characterized in that the elastic blade is made of a thermoplastic elastomer.
The developer regulating member according to the present invention is characterized in that the thermoplastic elastomer is a material selected from the group consisting of styrene-, olefin-, PVC-, urethane-, and polyamide-based elastomers.
The developer regulating member according to the present invention is characterized in that the resin injection gate is a tab gate, and a hot runner gate is formed on the tab gate.
The developer regulating member according to the present invention is characterized in that the resin injection gate is a tab gate, a subtab gate is formed on the tab gate, and a hot runner gate is formed on the subtab gate.
A method of molding a developer regulating member according to the present invention is characterized by comprising the steps of arranging a metal thin plate with spring elasticity adjacent to a cavity, for an elastic blade, in a mold, and injecting a thermoplastic elastomer from an injection sprue for the mold through a hot runner gate and a tab gate.
A method of molding a developer regulating member according to the present invention is characterized by comprising the steps of arranging a metal thin plate with spring elasticity adjacent to a cavity, for an elastic blade, in a mold, and injecting a thermoplastic elastomer from an injection sprue for the mold through a subtab gate, a hot runner gate, and a tab gate.
A method of molding a developer regulating member according to the present invention is characterized by further comprising, in addition to the step of arranging the metal thin plate in the cavity of the mold and injecting the thermoplastic elastomer, the step of compressing a surface of the elastic blade.
Other objects and advantages besides those discussed above shall be apparent to those skilled in the art from the description of a preferred embodiment of the invention which follows. In the description, reference is made to accompanying drawings, which form a part hereof, and which illustrate an example of the invention. Such example, however, is not exhaustive of the various embodiments of the invention, and therefore reference is made to the claims which follow the description for determining the scope of the invention.